Gas turbine engines (such as those used in electrical power generation or used in modern aircraft) typically include a compressor, a combustor section, and a turbine. The compressor and the turbine typically include a series of alternating rotors and stators. A rotor generally comprises a rotor disk and a plurality of blades. The rotor may be an integrally bladed rotor (“IBR”) or a mechanically bladed rotor.
The rotor disk and blades in the IBR are one piece (i.e., integral) with the blades spaced around the circumference of the rotor disk. Conventional IBRs may be formed using a variety of technical methods including integral casting, machining from a solid billet, or by welding or bonding the blades to the rotor disk. Conventional IBRs may include mistuned blades that respond differently at an engine stability pinch point. The “engine stability pinch point” is the engine operating point at which the remaining stability margin (available stability margin less the stability margin consumed by the sum of the external and internal destabilizing factors) is a relative medium. By making the blades have different responses because of their mistuning, the magnitude of a non-integral vibratory response (e.g., flutter) may be lessened. However, mistuned blades may reduce aerodynamic efficiency of the IBR. In addition, machining of an IBR may be difficult because of limited space between blades. For example, as engine cores (e.g., compressors and turbines) get smaller, the space between blades of an IBR shrinks, and the tooling does not shrink, so it is harder to machine the blades of IBRs as a machining head cannot fit between the blades.
Mechanically bladed rotors also have disadvantages. For example, the blades in a mechanically bladed fan rotor of a gas turbine engine may suffer from greater fan blade pull load because there is less rotor disk material to carry the pull load. Greater fan blade pull load increases stress levels on the rotor disk and thus on the rotor and potentially limits rotor life.